The present invention relates to a process for preparing dialkyl ketones by reductive carbonylation of xcex1-olefins by means of carbon monoxide and hydrogen in the presence of a catalyst system.
Dialkyl ketones are important solvents and intermediates for organic syntheses. Thus, in particular, 3-pentanone (diethyl ketone) is an excellent solvent for paints. Furthermore, 3-pentanone is used in numerous syntheses, for example the preparation of trimethylphenol and of vitamin E.
Dialkyl ketones are obtainable via a wide variety of synthetic routes, for instance by ketonization of carboxylic acids or aldehydes or by oxidation of secondary alcohols, of olefins or of alkanes. Disadvantages of these synthetic routes are the use of expensive intermediates (carboxylic acids, aldehydes, secondary alcohols, olefins having a central double bond) and often unsatisfactory selectivities and yields in the oxidation of olefins and alkanes.
A further synthetic route is reductive carbonylation of xcex1-olefins (olefins having a terminal double bond) in the presence of hydrogen, water or compounds having a reducing action, e.g. alcohols (cf. Ullmann""s Encyclopedia of Industrial Chemistry, 6th edition, 2000 electronic release, Chapter xe2x80x9cKETONESxe2x80x94Dialkyl Ketonesxe2x80x9d). A disadvantage of the use of water as hydrogen source is the additional consumption of stoichiometric amounts of carbon monoxide for binding the oxygen. A disadvantage of the use of compounds having a reducing action is the associated coproduction of the corresponding oxidation products.
In the reductive carbonylation of xcex1-olefins in the presence of carbon monoxide and hydrogen to form the corresponding dialkyl ketones, use is usually made of metals of groups 8 to 10 of the Periodic Table. DE-A 2 061 798 discloses carbonylation in the presence of cobalt carbonyl complexes and ammonia, an amine or a nitrile at a pressure of preferably from 4.5 to 140 atmospheres (from 0.45 to 14 MPa abs). U.S. Pat. No. 4,602,116 describes carbonylation in the presence of triruthenium dodecacarbonyl at a pressure of preferably from 1000 to 2500 psig (from 7 to 17.3 MPa abs). GB-A 2 208 480 discloses carbonylation in the presence of a ruthenium compound, a protic acid and a water-soluble solvent at a pressure of preferably from 5 to 7.5 MPa abs. DE-A 1 793 320 teaches carbonylation in the presence of a rhodium-containing catalyst at a pressure of from 200 to 300 atm (from 20 to 30 MPa abs). GB-A 2 202 165 describes carbonylation in the presence of a platinum(II) compound, a diphosphine and a protic acid at a pressure of preferably from 2 to 7.5 MPa abs.
Disadvantages of the abovementioned processes are the unsatisfactory stability of the catalyst systems and the high pressure necessary in carrying out the carbonylation.
EP-A 0 322 811 teaches the reductive carbonylation of xcex1-olefins to form the corresponding dialkyl ketones in the presence of a catalyst system comprising a rhodium complex, a phosphine and a para-substituted benzoic acid having an electron-withdrawing substituent in the para position. Disadvantages of the abovementioned process are the unsatisfactory selectivity (coproduction of aldehyde and ketone) and the (lack of) stability of the catalyst system.
SU-A 813 903 teaches the carbonylation of olefins in the presence of hydrogen to form the corresponding dialkyl ketones in the presence of palladium(II) acetate, triphenylphosphine and trifluoroacetic acid at atmospheric pressure. A selectivity of 50-98% is described for the synthesis of diethyl ketone. A disadvantage of this process is the very low activity of the catalyst system.
It is an object of the present invention to find a process for preparing dialkyl ketones which no longer has the above-described disadvantages, is based on economically attractive and readily available raw materials, avoids the formation of coproducts, utilizes a very stable, active and long-lived catalyst system and makes it possible to prepare dialkyl ketones in high yield even under mild reaction conditions.
We have found that this object is achieved by a process for preparing dialkyl ketones by reductive carbonylation of xcex1-olefins by means of carbon monoxide and hydrogen in the presence of a catalyst system comprising
(a) palladium or a palladium compound;
(b) a phosphine;
(c) a protic acid having a pKa of xe2x89xa64.5, measured in aqueous solution at 25xc2x0 C.; and
(d) a solubilizable carboxamide.
The presence of a solubilizable carboxamide is essential for the stability, activity and longevity of the catalyst system.
The carboxamides to be used in the process of the present invention are solubilizable in the reaction mixture and are also present in solubilized form under the reaction conditions. For the purposes of the present invention, the term xe2x80x9csolubilizedxe2x80x9d refers to a largely homogeneous distribution of the carboxamide in the reaction mixture, which is able to stabilize the catalyst system sufficiently. In general, the carboxamide is homogeneously dissolved in the reaction mixture or at least colloidally dispersed.
The carboxamides to be used in the process of the present invention have at least one carboxamide group of the formula xe2x80x94COxe2x80x94N less than  the molecule. The molar mass of the carboxamides can vary within a wide range from low molecular weight carboxamides having one carboxamide group in the molecule through to high molecular weight, polymeric carboxamides having a molecular weight of a few hundred thousand g/mol and a few hundred or a few thousand carboxamide groups in the molecule.
The chemical structure of the carboxamides to be used in the process of the present invention plays a minor role. Thus, the carboxamides can be, for example, saturated or unsaturated, aliphatic, aromatic or araliphatic compounds. Furthermore, the carboxamide can contain one or more heteroatoms such as oxygen, nitrogen, sulfur or phosphorus, for example xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94NHxe2x80x94, xe2x80x94NRxe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94COxe2x80x94Oxe2x80x94, xe2x80x94Nxe2x95x90, xe2x80x94COxe2x80x94N less than , xe2x80x94SiR2xe2x80x94, xe2x80x94PRxe2x80x94 and/or xe2x80x94PR2 and/or be substituted by one or more functional groups containing, for example, oxygen, nitrogen, sulfur and/or halogen atoms.
As carboxamides having one carboxamide group of the formula xe2x80x94COxe2x80x94N less than  in the molecule, preference is given to carboxamides of the formula (II) 
where the radicals Rxe2x80x2, Rxe2x80x3 and Rxe2x80x2xe2x80x3 are each, independently of one another,
hydrogen;
an acyclic or cyclic alkyl radical having from 1 to 30 carbon atoms which may contain one or more heteroatoms such as oxygen, nitrogen, sulfur or phosphorus, for example xe2x80x94Oxe2x80x94, xe2x80x94NHxe2x80x94, xe2x80x94NRxe2x80x94, xe2x80x94COxe2x80x94 and/or xe2x80x94COxe2x80x94Oxe2x80x94, and/or may bear one or more functional, aromatic or heteroaromatic groups containing, for example, oxygen, nitrogen, sulfur and/or halogen atoms, for example xe2x80x94OH, xe2x80x94CHO, xe2x80x94NH2, xe2x80x94COOH, xe2x80x94F, xe2x80x94Cl, xe2x80x94Br and/or xe2x80x94CN, as substituents, for example methyl, ethyl, 1-propyl, 2-propyl (sec-propyl), 1-butyl, 2-butyl (sec-butyl), 2-methyl-1-propyl (isobutyl), 2-methyl-2-propyl (tert-butyl), 1-pentyl, 2-pentyl, 3-pentyl, 3-methyl-2-butyl, 2-methyl-2-butyl, 1-hexyl, 1-heptyl, 1-octyl, 2-ethyl-1-hexyl, 1-nonyl, 1-decyl, 1-dodecyl, 1-tetradecyl, 1-hexadecyl, 1-octadecyl, 1-eicosyl, cyclopentyl, cyclohexyl, cyclooctyl, phenylmethyl (benzyl), 2-phenyl-1-ethyl; or
an aromatic radical having 1 or 2 aromatic rings and from 3 to 30 carbon atoms which may contain one or more heteroatoms, for example nitrogen, and/or may bear one or more functional or aliphatic groups containing, for example, oxygen, nitrogen, sulfur and/or halogen atoms, for example xe2x80x94OH, xe2x80x94CHO, xe2x80x94NH2, xe2x80x94COOH, xe2x80x94F, xe2x80x94Cl, xe2x80x94Br and/or xe2x80x94CN, as substituents, for example phenyl, 2-methylphenyl (2-tolyl), 3-methylphenyl (3-tolyl), 4-methylphenyl (4-tolyl), 2,4-dimethylphenyl, 2,6-dimethylphenyl, 2,4,6-trimethylphenyl, 1-naphthyl, 2-naphthyl.
Particularly preferred carboxamides having one carboxamide group of the formula xe2x80x94COxe2x80x94N less than in the molecule are carboxamides (II) in which the radicals Rxe2x80x2, Rxe2x80x3 and Rxe2x80x2xe2x80x3 are each, independently of one another,
a C1-C10-alkyl radical, for example methyl, ethyl, 1-propyl, 2-propyl (sec-propyl), 1-butyl, 2-butyl (sec-butyl), 2-methyl-1-propyl (isobutyl), 2-methyl-2-propyl (tert-butyl), 1-pentyl, 2-pentyl, 3-pentyl, 3-methyl-2-butyl, 2-methyl-2-butyl, 1-hexyl, 1-heptyl, 1-octyl, 2-ethyl-1-hexyl, 1-nonyl, 1-decyl; or
a phenyl radical which may be unsubstituted or substituted by from one to five C1-C6-alkyl groups, for example phenyl, 2-methylphenyl (2-tolyl), 3-methylphenyl (3-tolyl), 4-methylphenyl (4-tolyl), 2,4-dimethylphenyl, 2,6-dimethylphenyl, 2,4,6-trimethylphenyl.
Very particularly preferred carboxamides having one carboxamide group of the formula xe2x80x94COxe2x80x94N less than  in the molecule are N,N-dimethylacetamide, N,N-diethylacetamide, N,N-dipropylacetamide, N,N-diisopropylacetamide, N,N-dibutylacetamide, N,N-diisobutylacetamide, N,N-dipentylacetamide, N,N-dihexylacetamide, N,N-dioctylacetamide, N,N-dimethylpropionamide, N, N-diethylpropionamide, N, N-dipropylpropionamide, N,N-diisopropylpropionamide, N,N-dibutylpropionamide, N,N-diisobutylpropionamide, N,N-dipentylpropionamide, N,N-dihexylpropionamide and N,N-dioctylpropionamide.
As carboxamides having two or more carboxamide groups of the formula xe2x80x94COxe2x80x94N less than  in the molecule, it is generally possible to use monomeric, oligomeric or polymeric carboxamides in the process of the present invention.
Typical representatives of monomeric carboxamides having two or more carboxamide groups of the formula xe2x80x94COxe2x80x94N less than  in the molecule are the amides of dicarboxylic and oligocarboxylic acids, for example compounds of the formula
Rxe2x80x22Nxe2x80x94COxe2x80x94(CH2)nxe2x80x94COxe2x80x94NRxe2x80x22, 
where Rxe2x80x2 is as defined above and n is from 1 to 10.
For the purposes of the present invention, oligomeric and polymeric carboxamides are carboxamides which comprise linked structural repeating units of the same type or of different types and in which at least one of these linked structural repeating units contains a carboxamide group of the formula xe2x80x94COxe2x80x94N less than  and the overall oligomer or polymer contains at least two carboxamide groups of the formula xe2x80x94COxe2x80x94N less than . The dividing line between oligomeric and polymeric is not defined exactly in the relevant literature. However, the division is generally made at a molar mass of about 10,000 g/mol. The upper limit of the molar mass of the polymeric carboxamides to be used in the process of the present invention is determined by the condition of solubilizability in the reaction mixture. It is generally, depending on the type of chemical structure, from about 1000 to 200,000 g/mol.
In the process of the present invention, preference is given to using an oligomeric or polymeric carboxamide containing at least 5 carboxamide groups of the formula xe2x80x94COxe2x80x94N less than  and having a molar mass in the range from 1000 to 200,000 g/mol, preferably from 5000 to 100,000 g/mol and particularly preferably from 10,000 to 100,000 g/mol. The molar mass specified is in each case a mean molar mass since the preparation of the polyamines and their further reaction usually results in a broad molar mass distribution.
The oligomeric and polymeric carboxamides are generally homooligomers, cooligomers, homopolymers and copolymers of nitrogen-containing monomer units. Suitable examples are
acylated oligoalkylenimines and polyalkylenimines, in particular acylated oligoethylenimines and polyethylenimines;
acylated oligovinylamines and polyvinylamines;
oligomers and polymers of ethylenically unsaturated carboxamides, for example oligoacrylamides and polyacrylamides or oligomethacrylamides and polymethacrylamides; and
oligomers and polymers of acyclic and cyclic N-vinyl amides, for example oligovinylformamides and polyvinylformamides or oligovinylcaprolactams and polyvinylcaprolactams.
The oligomers and polymers may have different nitrogen-containing monomers and, if desired, nitrogen-free monomers in one molecule. The carboxamide group of the formula xe2x80x94COxe2x80x94N less than  may be present in the main chain or in side groups.
The polarity of the oligomeric or polymeric carboxamide is chosen so that it is present in solubilized form in the reaction mixture under the reaction conditions. The presence of the carboxamide groups alone achieves an appropriate polarity. It can be increased further by means of further suitable substituents. In the case of amino-containing oligomers and polymers, the polarity can be increased, for example, by means of additional substituents such as alkyl, aryl or polyoxyalkylene groups. The introduction of substituents can be carried out by reaction with suitable derivative-forming reagents, e.g. carboxylic acids, carboxylic acid derivatives, alkylating agents or alkene oxides, by phosphonomethylation, by the Strecker synthesis, etc. Derivative formation can occur at nitrogen atoms or in other positions on the oligomer or polymer. The functional groups can be introduced by polymer-analogous reaction of the nitrogen-containing oligomer or polymer or at the stage of the pair of monomers or by concomitant use of suitable copolymerizable nitrogen-free monomers.
As component (d) in the process of the present invention, particular preference is given to using an acylated oligoethylenimine or polyethylenimine comprising units of the formula (I) or branched isomers thereof 
where the sum m+n is at least 10 and A are each, independently of one another, hydrogen or a xe2x80x94COxe2x80x94R group, where R are each, independently of one another, an alkyl, cycloalkyl, aryl, aralkyl or acyl radical having up to 30 carbon atoms. The ratio m/(m+n) is preferably from 0.01 to 1.
The sum m+n is preferably at least 50 and particularly preferably at least 100. The ratio m/(m+n) is preferably from 0.3 to 1 and particularly preferably from 0.5 to 0.9.
The acylated oligoethyleneimines or polyethyleneimines (I) which are preferably used generally contain primary (xe2x80x94NH2), secondary ( greater than NH) and tertiary ( greater than Nxe2x80x94) amino groups. The ratio of primary:secondary:tertiary amino groups is generally 1:0.1-2:0.1-2 and preferably 1:0.8-1.3:0.6-1.1.
The acylated oligoethyleneimines or polyethyleneimines (I) which are preferably used comprise the following structural elements or branched isomers thereof 
where R is as defined above.
The radical R is preferably
an unbranched or branched, substituted or unsubstituted C1-C21-alkyl radical such as methyl, ethyl, 1-propyl, 2-propyl (sec-propyl), 1-butyl, 2-butyl (sec-butyl), 2-methyl-1-propyl (isobutyl), 2-methyl-2-propyl (tert-butyl), 1-pentyl, 2-pentyl, 3-pentyl, 1-hexyl, 1-heptyl, 2-heptyl, 3-heptyl, 1-octyl, 2,4,4-trimethylpentyl, 1-nonyl, 2-methyl-2-octyl, 1-decyl, 1-undecyl, 1-dodecyl, 1-tridecyl, 1-tetradecyl, 1-pentadecyl, 1-hexadecyl, 1-heptadecyl, 1-octadecyl, 1-nonadecyl, 1-eicosyl or 1-heneicosyl;
an unbranched or branched, substituted or unsubstituted cycloalkyl radical having from 5 to 20 carbon atoms, for example cyclopentyl, cyclohexyl or cyclooctyl;
a phenyl radical which may be unsubstituted or substituted by from one to five C1-C8-alkyl groups, for example phenyl, 2-methylphenyl (2-tolyl), 3-methylphenyl (3-tolyl), 4-methylphenyl (4-tolyl), 2,4-dimethylphenyl, 2,6-dimethylphenyl and 2,4,6-trimethylphenyl;
a substituted or unsubstituted aralkyl radical having from 7 to 20 carbon atoms, for example phenylmethyl (benzyl) or 2-phenyl-1-ethyl.
The R is particularly preferably a C1-C6-alkyl radical such as methyl, ethyl, 1-propyl, 2-propyl (sec-propyl), 1-butyl, 2-butyl (sec-butyl), 2-methyl-1-propyl (isobutyl), 2-methyl-2-propyl (tert-butyl), 1-pentyl, 2-pentyl, 3-pentyl or 1-hexyl.
The component (d) used in the process of the present invention is very particularly preferably an acylated oligoethylenimine or polyethylenimine (I) in which the acyl radical Rxe2x80x94COxe2x80x94 corresponds to the acyl radical of the carboxylic acid which can be obtained from the xcex1-olefin used, carbon monoxide and water in the presence of the same catalyst system. When the simplest xcex1-olefin, viz. ethene, is used, Rxe2x80x94COxe2x80x94 is thus very particularly preferably a propionyl radical CH3CH2xe2x80x94COxe2x80x94.
Oligoethylenimines and polyethylenimines are generally prepared by homopolymerization or copolymerization of aziridine, if appropriate together with other monomers such as vinyl amides, vinylamines, acrylamides, acrylamines, acrylic esters, methacrylic esters and olefins such as ethene, propene, butene or butadiene, and generally have a mean molecular weight of from 200 to 200,000 g/mol.
The particularly preferred acylated oligoethylenimines and polyethylenimines (I) are generally prepared by reaction of the oligoethylenimines and polyethylenimines with carboxylic acids, for example formic acid, acetic acid, propionic acid, butyric acid, valeric acid, lauric acid, 2-ethylhexanoic acid or natural C18-fatty acids, with the degree of amidation being from 1 to almost 100%, preferably from 30 to almost 100%, based on the amidatable amino groups. Details of the preparation may be found in DE-A 37 27 704. However, it is also possible to prepare the acylated oligoethylenimines and polyethylenimines (I) in situ under the carbonylation conditions, for example by reaction of an oligoethylenimine or polyethylenimine with an olefin and carbon monoxide in the presence of the nucleophilic compound, the palladium component and the phosphine or by reaction of the polyethylenimine with the carboxylic acid used as solvent under the conditions of the carbonylation reaction.
Furthermore, the acylated oligoethylenimine or polyethylenimine (I) may further comprise structural elements of the type 
where the radical Rx is defined as for the radical R or is a hydroxyalkyl(poly)oxyalkylene radical having up to 500 oxyalkylene units and preferably having from 2 to 6 carbon atoms per oxyalkylene unit. They are generally prepared by reacting the acylated oligoethylenimines and polyethylenimines with up to 500 mol of ethylene oxide, propylene oxide or butylene oxide per monomer unit of the oligoethylenimine or polyethylenimine. Details of the preparation may be found in U.S. Pat. No. 5,846,453.
The structure shown in the above formula (I) is an idealized formula for the case where the acylated oligoethylenimines and polyethylenimines shown are linear. The repeating units can be present in any order, for example a random order. The acylated oligoethylenimines and polyethylenimines to be used in the process of the present invention may also be partly branched and have, for example, structural elements of the type shown below: 
If in the present text reference is made to xe2x80x9cbranched isomersxe2x80x9d in the context of oligoethylenimines and polyethylenimines, this refers to structural isomers derived from the structure shown by single or multiple insertion of one of the repeating units shown in brackets in formula (I) into an NH bond. They are branched via tertiary nitrogen atoms.
Further compounds suitable as component (d) in the process of the present invention are acylated oligovinylamines and polyvinylamines of the formula (III) 
where m and n are as defined above and R are, independently of one another, as defined under (I).
Further compounds suitable as component (d) in the process of the present invention are oligoacrylamides and polyacrylamides and oligomethacrylamides and polymethacrylamides comprising, as characteristic structural element, units of the formula (IV) 
where Ra is hydrogen or methyl, R are, independently of one another, as defined under (I) and m and n are as defined above.
In general, preference is given to solubilizable nitrogen-containing polymers which are free of sulfonic acid groups.
In the process of the present invention, the carboxamide (d) is generally used in an amount of from 0.5 to 15% by weight, preferably from 1 to 10% by weight and particularly preferably from 3 to 7.5% by weight, based on the total mass of the initial reaction mixture, i.e. at the beginning of the reaction.
Possible palladium sources for component (a) in the process of the present invention are inorganic and organic salts of palladium, palladium compounds containing nitrogen-, phosphorus- and/or oxygen-containing donor ligands and also palladium or palladium compounds applied to a support. Preference is given to halogen-free palladium sources.
Examples of suitable inorganic and organic salts of palladium are palladium(II) nitrate, palladium(II) sulfate, palladium(II) carboxylates (e.g. palladium(II) acetate or palladium(II) propionate), palladium(II) sulfonates and palladium(II) acetylacetonate.
Examples of suitable palladium compounds containing nitrogen-, phosphorus- and/or oxygen-containing donor ligands are tetrakis(triphenylphosphine)palladium(0) (Pd(PPh3)4), dibenzylideneacetonepalladium(0) (Pd(dba)2) or [Pd(dpa-3)(CH3CN)2] [A]2, where A is a weakly coordinating anion, for example chlorate, hexafluorophosphate, tetrafluoroborate or p-toluenesulfonate, and xe2x80x9cdpa-3xe2x80x9d is 1,3-P,Pxe2x80x2-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo [3.3.1.1{3.7}]decyl)propane.
A suitable example of palladium applied to a support is palladium on activated carbon. Palladium sources of this type are preferably used as particles which allow suspension in the reaction mixture. The support materials are preferably hydrophilic in nature to ensure a stable suspension and may be made hydrophilic by separate measures such as surface oxidation of activated carbon.
In the process of the present invention, the palladium or the palladium compound (a) is generally used in an amount of from 0.5 to 20 mmol of palladium per liter of initial reaction mixture.
Phosphines (b) suitable for use in the process of the present invention are described, for example, in EP-A 0 274 795, EP-A 0 282 142, EP-A 0 386 833, EP-A 0 441 446, EP-A 0 495 547, EP-A 0 495 548, EP-A 0 499 329, EP-A 0 577 204, EP-A 0 577 205, WO 94/18154, WO 96/19434, WO 96/45040 and WO 98/42717, which are hereby expressly incorporated by reference. The suitable phosphines have the formula (V)
PR1R2R3 xe2x80x83xe2x80x83(V) 
where the radicals R1, R2 and R3 are each, independently of one another, a carbon-containing organic radical. The radicals R1, R2 and/or R3 may also be joined to one another.
For the present purposes, a carbon-containing organic radical is an unsubstituted or substituted, aliphatic, aromatic or araliphatic radical having from 1 to 30 carbon atoms. This radical can also contain one or more heteroatoms such as oxygen, nitrogen, sulfur or phosphorus, for example xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94NRxe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94Nxe2x95x90, xe2x80x94SiR2xe2x80x94, xe2x80x94PRxe2x80x94 and/or xe2x80x94PR2, and/or be substituted by one or more functional groups containing, for example, oxygen, nitrogen, sulfur and/or halogen atoms, for example by fluorine, chlorine, bromine, iodine and/or a cyano group (here, the radical R is likewise a carbon-containing organic radical). If the carbon-containing organic radical contains one or more heteroatoms, it can also be bound via a heteroatom. Thus, for example, ether, thioether and tertiary amino groups are also included. The carbon-containing organic radical can be a monovalent or polyvalent, for example divalent, radical.
If the phosphine (V) contains precisely one phosphorus atom, i.e. the radicals R1, R2 and R3 contain neither a xe2x80x94PRxe2x80x94 group nor a xe2x80x94PR2xe2x80x94 group, this will hereinafter be referred to as a monodentate phosphine. If R1, R2 and/or R3 contain one or more xe2x80x94PRxe2x80x94 or xe2x80x94PR2xe2x80x94 groups, the phosphines (V) are referred to as bidentate, tridentate, etc., depending on the number of phosphorus atoms.
In the process of the present invention, preference is given to using a phosphine which is at least bidentate. It can be described by the formula (VI) 
where the radicals R4, R5, R6 and R7 are each, independently of one another, a carbon-containing organic radical and X is a carbon-containing organic bridging group. The preferred phosphines (VI) are bidentate, tridentate or tetradentate, in particular bidentate.
The term carbon-containing organic radical is defined as set forth above.
For the present purposes, a carbon-containing organic bridging group is an unsubstituted or substituted, aliphatic, aromatic or araliphatic divalent group having from 1 to 20 carbon atoms and from 1 to 10 atoms in the chain. The organic bridging group may contain one or more heteroatoms such as oxygen, nitrogen, sulfur or phosphorus, for example xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94NRxe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94Nxe2x95x90, xe2x80x94SiR2xe2x80x94, xe2x80x94PRxe2x80x94 and/or xe2x80x94PR2, and/or be substituted by one or more functional groups containing, for example, oxygen, nitrogen, sulfur and/or halogen atoms, for example by fluorine, chlorine, bromine, iodine and/or a cyano group (here, the radical R is likewise a carbon-containing organic radical). If the organic bridging group contains one or more heteroatoms, it can also be bound via a heteroatom. Thus, for example, ether, thioether and tertiary amino groups are also included.
Monovalent radicals R1, R2 and R3 in formula (V) and R4, R5, R6 and R7 in formula (VI) are each preferably
an unbranched or branched, acyclic or cyclic, unsubstituted or substituted alkyl radical having from 1 to 20 aliphatic carbon atoms in which one or more of the CH2 groups may also be replaced by heteroatoms such as xe2x80x94Oxe2x80x94 or xe2x80x94Sxe2x80x94 or by heteroatom-containing groups such as xe2x80x94COxe2x80x94, xe2x80x94NRxe2x80x94 or xe2x80x94SiR2xe2x80x94, and in which one or more of the hydrogen atoms may be replaced by substituents such as aryl groups; or
an unsubstituted or substituted aromatic radical which contains one ring or two or three fused rings and in which one or more ring atoms may be replaced by heteroatoms such as nitrogen and one or more of the hydrogen atoms may be replaced by substituents such as alkyl or aryl groups.
Examples of preferred monovalent radicals are unsubstituted or substituted C1-C20-alkyl, C5-C20-cycloalkyl, C6-C20-aryl and C3-C20-heteroaryl radicals, for example methyl, ethyl, 1-propyl, 2-propyl (sec-propyl), 1-butyl, 2-butyl (sec-butyl), 2-methyl-1-propyl (isobutyl), 2-methyl-2-propyl (tert-butyl), 1-pentyl, 2-pentyl, 3-pentyl, 2-methyl-2-butyl (tert-amyl), 1-hexyl, 2-hexyl, 3-hexyl, 2-methyl-2-pentyl, 3-methyl-3-pentyl, 2-methoxy-2-propyl, cyclopentyl, cyclohexyl, cyclooctyl, phenyl, 2-methylphenyl (o-tolyl), 3-methylphenyl (m-tolyl), 4-methylphenyl (p-tolyl), 2,6-dimethylphenyl, 2,4-dimethylphenyl, 2,4,6-trimethylphenyl, 2-methoxyphenyl, 3-methoxyphenyl, 4-methoxyphenyl, 2-pyridyl, 3-pyridyl, 4-pyridyl, 3-pyridazinyl, 4-pyridazinyl, 5-pyridazinyl, 2-pyrimidinyl, 4-pyrimidinyl, 5-pyrimidinyl, 2-pyrazinyl, 2-(1,3,5-triazin)yl, 1-naphthyl, 2-naphthyl, 2-quinolyl, 8-quinolyl, 1-isoquinolyl and 8-isoquinolyl.
Divalent radicals R1 together with R2, R2 together with R3 or R1 together with R3 in formula (V) and R4 together with R5 and/or R6 together with R7 in formula (VI) are each preferably
an unbranched or branched, acyclic or cyclic, unsubstituted or substituted C4-C20-alkylene radical (xe2x80x9cdivalent alkyl radicalxe2x80x9d) which has from 4 to 10 atoms in the alkylene chain and in which CH2 groups may also be replaced by heterogroups, for example xe2x80x94COxe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94SiR2xe2x80x94 or xe2x80x94NRxe2x80x94, and in which one or more of the hydrogen atoms may be replaced by substituents such as aryl groups.
Examples of preferred divalent radicals are unsubstituted or substituted C4-C30-alkylene radicals in which CH2 groups may be replaced by hetero groups such as xe2x80x94Oxe2x80x94, for example 1,4-butylene, 1,4-dimethyl-1,4-butylene, 1,1,4,4-tetramethyl-1,4-butylene, 1,4-dimethoxy-1,4-butylene, 1,4-dimethyl-1,4-dimethoxy-1,4-butylene, 1,5-pentylene, 1,5-dimethyl-1,5-pentylene, 1,5-dimethoxy-1,5-pentylene, 1,1,5,5-tetramethyl-1,5-pentylene, 1,5-dimethyl-1,5-dimethoxy-1,5-pentylene, 3-oxa-1,5-pentylene, 3-oxa-1,5-dimethyl-1,5-pentylene, 3-oxa-1,5-dimethoxy-1,5-pentylene, 3-oxa-1,1,5,5-tetramethyl-1,5-pentylene, 3-oxa-1,5-dimethyl-1,5-dimethoxy-1,5-pentylene, 1,4-cyclooctylene, 1,5-cyclooctylene, 1,4-dimethyl-1,4-cyclooctylene, 1,4-dimethyl-1,5-cyclooctylene, 1,4-dimethyl-5,8-cyclooctylene, 1,5-dimethyl-1,4-cyclooctylene, 1,5-dimethyl-1,5-cyclooctylene, 1,5-dimethyl-4,8-cyclooctylen, 
3,7-bicyclo[3.3.1]nonylene, 
1,3,5,7-tetramethyl-3,7-bicyclo[3.3.1]nonylene, 
1,3,5,7-tetramethyl-4,8,9-trioxa-3,7-bicyclo[3.3.1]nonylene.
Trivalent radicals R1 together with R2 together with R3 are each preferably
an unbranched or branched, acyclic or cyclic, unsubstituted or substituted trivalent alkyl radical which has from 4 to 20 carbon atoms and in each case from 4 to 10 atoms in the chain and in which CH2 groups may also be replaced by heterogroups, for example xe2x80x94COxe2x80x94, xe2x80x94Oxe2x80x94 or xe2x80x94NRxe2x80x94, and in which one or more of the hydrogen atoms may be replaced by substituents such as aryl groups.
The phosphine (V) or (VI) to be used in the process of the present invention particularly preferably encompasses compounds in which
the radicals R1, R2 and/or R3 and R4, R5, R6 and/or R7 are each, independently of one another, an unsubstituted or substituted C3-C12-alkyl radical in which at least two, preferably three, further skeletal atoms are bound to the xcex1-carbon atom or an unsubstituted or substituted aromatic radical which has six ring atoms and in which one, two or three ring atoms can also be replaced by nitrogen; and/or
the radicals R1 together with R2, R2 together with R3 or R1 together with R3 and also R4 together with R5 and/or R6 together with R7 are in each case, independently of one another, an unsubstituted or substituted C4-C30-alkylene radical which has from 4 to 7 atoms in the shortest alkylene chain and in which CH2 groups may be replaced by heterogroups, for example by xe2x80x94Oxe2x80x94.
For the present purposes, the term skeletal atoms refers to the skeleton-forming atoms such as carbon, oxygen or nitrogen.
Examples of particularly preferred monovalent radicals R1, R2 and/or R3 and also R4, R5, R6 and/or R7 are 2-propyl (sec-propyl), 2-butyl (sec-butyl), 2-methyl-2-propyl (tert-butyl), 2-methyl-2-butyl (tert-amyl), phenyl, 2-methylphenyl (o-tolyl), 3-methylphenyl (m-tolyl), 4-methylphenyl (p-tolyl), 2,6-dimethylphenyl, 2,4-dimethylphenyl, 2,4,6-trimethylphenyl and 2-pyridyl, in particular 2-methyl-2-propyl (tert-butyl) and phenyl. Examples of particularly preferred divalent radicals R1 together with R2, R2 together with R3 or R1 together with R3 and also R4 together with R5 and/or R6 together with R7 are 1,1,4,4-tetramethyl-1,4-butylene, 1,4-dimethyl-1,4-dimethoxy-1,4-butylene, 1,1,5,5-tetramethyl-1,5-pentylene, 1,5-dimethyl-1,5-dimethoxy-1,5-pentylene, 1,5-dimethyl-1,5-cyclooctylene, 1,3,5,7-tetramethyl-3,7-bicyclo[3.3.1]nonylene and 1,3,5,7-tetramethyl-4,8,9-trioxa-3,7-bicyclo[3.3.1]nonylene, in particular 1,3,5,7-tetramethyl-4,8,9-trioxa-3,7-bicyclo[3.3.1]nonylene.
The organic bridging group X in formula (VI) is preferably an unbranched or branched, acyclic or cyclic, unsubstituted or substituted divalent aliphatic, aromatic or araliphatic group which has from 1 to 20 carbon atoms and from 1 to 8 atoms, preferably from 2 to 4 atoms, in the chain and in which one or more of the CH2 groups may be replaced by heteroatoms such as xe2x80x94Oxe2x80x94 or by heteroatom-containing groups such as xe2x80x94COxe2x80x94 or xe2x80x94NRxe2x80x94, and/or one or more of the aromatic ring atoms may be replaced by heteroatoms such as nitrogen, and in which one or more of the hydrogen atoms may be replaced by substituents such as alkyl or aryl groups.
Examples of preferred bridging groups X are 1,2-ethylene, 1,3-propylene, 1,2-propylene, 1,4-butylene, 2-methyl-1,3-propylene, 1,5-pentylene, 2,2-dimethyl-1,3-propylene, 1,6-hexylene, xe2x80x94Oxe2x80x94CH2CH2xe2x80x94Oxe2x80x94, xe2x80x94Oxe2x80x94CH2CH2CH2xe2x80x94Oxe2x80x94, xe2x80x94CH2xe2x80x94Oxe2x80x94CH2xe2x80x94, xe2x80x94CH2CH2xe2x80x94Oxe2x80x94CH2CH2xe2x80x94, o-phenylene, o-xylene and xe2x80x94CH2xe2x80x94NRxe2x80x94CH2xe2x80x94, in particular 1,2-ethylene, 1,3-propylene, 1,4-butylene and o-xylene.
A particularly preferred monodentate phosphine is triphenylphosphine. Particularly preferred bidentate phosphines are 1,2-bis(di-tert-butylphosphino)ethane, 1,2-bis(diphenylphosphino)ethane, 1,2-P,Pxe2x80x2-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo-[3.3.1.1{3.7}]decyl)ethane (xe2x80x9cdpa-2xe2x80x9d for short), 1,3-bis(di-tert-butylphosphino)propane, 1,3-bis(diphenylphosphino)propane, 1,3-P,Pxe2x80x2-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo-[3.3.1.1{3.7}]decyl)propane (xe2x80x9cdpa-3xe2x80x9d for short), 1,4-bis(di-tert-butylphosphino)butane, 1,4-bis(diphenylphosphino)butane, 1,4-P,Pxe2x80x2-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo-[3.3.1.1{3.7}]decyl)butane (xe2x80x9cdpa-4xe2x80x9d for short), xcex1,xcex1xe2x80x2-bis(di-tert-butylphosphino)-o-xylene, xcex1,xcex1xe2x80x2-bis(diphenylphosphino)-o-xylene and xcex1,xcex1-P,Pxe2x80x2-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo-[3.3.1.1{3.7}]decyl)-o-xylene, in particular 1,3-bis(di-tert-butylphosphino)propane, 1,3-bis(diphenylphosphino)propane and 
1,3-P,Pxe2x80x2-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo[3.3.1.1{3.7}]decyl)propane (xe2x80x9cdpa-3xe2x80x9d).
In the process of the present invention, the phosphine (b) is generally used in a molar ratio to palladium of from 0.5 to 50. When using a monodentate phosphine ligand, its molar ratio to palladium is preferably in the range from 4 to 30, and when using a bidentate phosphine ligand, its molar ratio to palladium is preferably in the range from 1 to 20.
When using monodentate phosphine ligands, preference is given to using from 5 to 20 mmol, particularly preferably from 5 to 10 mmol, of palladium per liter of initial reaction mixture, and when using bidentate phosphine ligands, preference is given to using from 0.5 to 5 mmol, particularly preferably from 1 to 3 mmol, of palladium per liter of initial reaction mixture.
As component (c) in the process of the present invention, use is made of a protic acid having a pKa of xe2x89xa64.5, measured in aqueous solution at 25xc2x0 C.
The protic acid to be used can be an organic or inorganic protic acid. Preference is given to protic acids which form a weakly coordinating or noncoordinating anion.
Examples of suitable protic acids are
strong mineral acids such as sulfuric acid, phosphoric acid (either orthophosphoric or pyrophosphoric acid), perchloric acid and tetrafluoroboric acid;
sulfonic acids such as methanesulfonic acid, trifluoromethanesulfonic acid, chlorosulfonic acid, fluorosulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, naphthalenesulfonic acid and ion-exchange resins containing sulfonic acid groups; and
carboxylic acids such as oxalic acid, glycolic acid, chloroacetic acid, dichloroacetic acid, trichloroacetic acid and trifluoroacetic acid.
In the process of the present invention, preference is given to using protic acids (c) having a pKa of xe2x89xa62, measured in aqueous solution at 25xc2x0 C.
Preferred protic acids are p-toluenesulfonic acid, methanesulfonic acid, trifluoromethanesulfonic acid, trichloroacetic acid and trifluoroacetic acid.
The molar ratio of the protic acid (c) to the palladium (a) is generally not critical. It is generally in the range from 0.5 to 5000, preferably from 10 to 3000.
The catalyst system to be used in the process of the present invention can be homogeneous or heterogeneous. When using a homogeneous catalyst system, the catalyst system is solubilized in the reaction mixture and is generally homogeneously distributed. When using a heterogeneous catalyst system, the catalyst system or its precursor is generally present in particulate form. An example of this is palladium or a palladium compound deposited on a support material as component (a).
The process of the present invention is preferably carried out in a liquid phase. In this case, the catalyst system is generally solubilized substantially homogeneously in the reaction mixture. In general, the liquid carbonylation product and the protic acid used serve as solvent. However, it is also possible to carry out the reductive carbonylation in a preferred inert solvent. Solvents which are well suited for this purpose are, for example, aromatic or aliphatic hydrocarbons such as toluene, xylene or decalin and polar, aprotic solvents such as tetrahydrofuran, 1,4-dioxane, N-methylpyrrolidone, N-methylpiperidone, dimethyl sulfoxide, glycol ethers (e.g. 1,2-dimethoxyethane, bis(2-methoxyethyl) ether or bis(2-butoxyethyl) ether), dimethylformamide, dimethylformanilide, ethylene carbonate, propylene carbonate, ketones (e.g. acetone or diethyl ketone) or mixtures thereof. The process is preferably carried out in a solvent corresponding to the carbonylation product, since this introduces no further extraneous components into the system.
In the process of the present invention, the catalyst system can generally be obtained by combining the above-described components (a), (b), (c), (d) and any solvent to be used in any order. This also encompasses the use of intermediates, e.g. palladium-phosphine complexes.
For the purposes of the present invention, xcex1-olefins are unsubstituted or substituted alkenes having at least one terminal double bond of the structure xe2x80x94CHxe2x95x90CH2. Possible substituents for the part of the molecule adjacent to the terminal double bond are, for example, aryl groups, heteroaryl groups, halides or functional groups, e.g. xe2x80x94COOH, xe2x80x94COOR, xe2x80x94CONR2, xe2x80x94CN or xe2x80x94OR. The xcex1-olefins generally have from 2 to 30 carbon atoms. In addition to the terminal double bond, further carbonxe2x80x94carbon double bonds may also be present in the molecule.
The xcex1-olefin used in the process of the present invention is preferably a C2-C20-alkene having a terminal double bond, for example ethene, propene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene and 1-decene. Particular preference is given to ethene, propene, 1-butene, 1-pentene and 1-hexene, in particular ethene.
The process of the present invention generally forms, except in the case of the simplest dialkyl ketone which can be prepared in the process, viz. 3-pentanone, a mixture of two isomers of the corresponding dialkyl ketone 
where the radical R* in the simplified reaction equation above is determined according to the above definition of the xcex1-olefin R*xe2x80x94CHxe2x95x90CH2 to be used. Thus, use of ethene results in formation of 3-pentanone (R* corresponds to hydrogen) and use of propene results in formation of a mixture of 4-heptanone and 2-methyl-3-hexanone (R* corresponds to methyl).
The preparation of 3-pentanone is particularly preferred in the process of the present invention.
The process of the present invention is generally carried out at from 40 to 200xc2x0 C., preferably from 75 to 170xc2x0 C., particularly preferably from 80 to 130xc2x0 C. The pressure in the process of the present invention is generally from 0.1 to 20 MPa abs, preferably from 0.5 to 7 MPa abs, particularly preferably from 1 to 2.5 MPa abs.
The process of the present invention can be carried out batchwise, semicontinuously or continuously.
When the process of the present invention is carried out batchwise, the order of addition of the starting materials xcex1-olefin, carbon monoxide and hydrogen is generally unimportant. When the process is carried out semicontinuously or continuously, the starting materials are preferably added in the stoichiometrically required ratio, i.e. xcex1-olefin:CO:H2=2:1:1.
In a general embodiment, the catalyst system or its precursor is prepared by combining the components (a) palladium or a palladium compound, (b) phosphine, (c) protic acid having a pKa of xe2x89xa64.5, (d) solubilizable carboxamide and any solvent to be used in any order.
In a general embodiment of a batchwise process, the catalyst system or its precursor is admixed in a suitable reaction apparatus (e.g. an autoclave) with the starting materials xcex1-olefin, carbon monoxide and hydrogen and the system is maintained under reaction conditions (pressure, temperature). After the reaction is complete, the apparatus is cooled, depressurized and the reaction product is worked up in a customary fashion, e.g. by distillation.
In a general embodiment of a semicontinuous process, the catalyst system or its precursor is admixed in a suitable reaction apparatus (e.g. an autoclave) with none, with one, two or all three, depending on the embodiment, of the starting material components and the system is brought to the reaction conditions (temperature, pressure). To set the pressure, the gaseous starting materials carbon monoxide, hydrogen and/or the xcex1-olefin (if gaseous) are introduced. Subsequently, the necessary starting materials are introduced continuously or periodically during the course of the reaction in amounts corresponding to those in which they are consumed, preferably in the stoichiometrically required ratio. After the reaction is complete, the apparatus is cooled, depressurized and the reaction product is worked up in a customary fashion, e.g. by distillation.
In a general embodiment of a continuous process, the catalyst system or its precursor is admixed in a suitable reaction apparatus (e.g. an autoclave) with none, with one, two or all three, depending on the embodiment, starting material components and the system is brought to the reaction conditions (temperature, pressure). To set the pressure, the gaseous starting materials carbon monoxide, hydrogen and/or the xcex1-olefin (if gaseous) are introduced. Subsequently, the three starting materials are fed in continuously in amounts corresponding to those in which they are consumed, preferably in the stoichiometrically required ratio, and a corresponding amount of the reaction mixture is continuously discharged from the reaction apparatus for work-up.
In a preferred embodiment of the continuous preparation of 3-pentanone, palladium(II) acetate, the bidentate phosphine ligand xe2x80x9cdpa-3xe2x80x9d (1,3-P,Pxe2x80x2-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo-[3.3.1.1{3.7}]decyl)propane), a protic acid having a pKa of xe2x89xa62 and a polyethylenimine polymer amidated with propionic acid are placed in a suitable reaction apparatus, for example a bubble column, the mixture is brought to the desired reaction temperature and to the desired reaction pressure by introduction of carbon monoxide, hydrogen and ethene. The three starting materials ethene, carbon monoxide and hydrogen are subsequently fed in continuously in the stoichiometrically required ratio. The 3-pentanone formed can then, for example, be removed continuously from the reaction apparatus by stripping it out by means of a suitable gas stream (e.g. ethene/carbon monoxide/hydrogen mixture).
The process of the present invention makes it possible to prepare dialkyl ketones in high yield from economically attractive and readily available raw materials under mild reaction conditions. The catalyst system used has a high catalytic activity and a high stability in respect of precipitation of palladium and palladium compounds. Furthermore, the process forms no undesirable coproducts. In addition, the use of the preferred oligomeric or polymeric carboxamide makes it possible for the carbonylation product to be separated from the reaction mixture in a technically simple manner, which is a decisive advantage.